Field of the Disclosure
The present invention relates to shift registers for the gate driving circuit of the liquid crystal display device, and more particularly to a shift register which can reduce power consumption.
Discussion of the Related Art
Recently, a GIP (Gate In Panel) type liquid crystal display device is introduced, in which a gate driving circuit is mounted in a panel thereof for reducing volume and weight of the display device.
In the GIP type liquid crystal display device, the gate driving circuit is mounted in a non-display region of the panel so as to realize a small volume, weight reduction and low manufacturing cost. The gate driving circuit includes a shift register for sequentially supplying scan pulses to a plurality of gate lines of the liquid crystal display panel. The shift register has an output buffer unit for receiving a clock pulse from a timing controller and outputting a scan pulse to the gate line, and an output control unit for controlling the output of the output buffer unit. A Thin Film Transistor (TFT) formed of amorphous silicon (a-Si) is used as the output buffer unit.P=IV=CV2f  (1)
At this time, the power consumption of the TFT configuring the output buffer unit is greatest in the gate driving circuit. In detail, referring to equation 1, the power consumption P is proportional to a current I, a voltage V, capacitance C, and a frequency f. The output buffer unit receives a clock pulse having a fastest driving frequency. And, the TFT of the output buffer unit has a greatest size in the gate driving circuit, resulting to have a greatest capacitance C of a parasitic capacitor generated between a gate electrode and a first electrode (source electrode) which receives the clock pulse in the TFT.
Accordingly, since the TFT configuring the output buffer unit has highest driving frequency f and greatest capacitance C of the parasitic capacitor, the power consumption of the TFT is greatest in the gate driving circuit.
Generally, a display device using a gate driving integrated circuit also includes an output buffer unit similarly to the GIP type liquid crystal display device. In the gate driving integrated circuit, the output buffer unit has a TFT formed of a polysilicon, and the capacitance C of a parasitic capacitor of the polysilicon TFT is less than that of an amorphous silicon TFT.
Thus, the GIP type liquid crystal display device has a problem in that power consumption is greater than a display device which uses a gate driving IC having the polysilicon TFT due to the output buffer unit of the gate driving circuit.